Conventional abrasivejet technology is used to cut a variety of materials but is found to be highly inefficient in the use of energy and resources mainly due to equipment design limitations that incorporate use of garnet as the abrasive. Conventional abrasivejet is also currently limited to perform one purpose at a time such as thru cutting of material or surface removal of material as there are not any abrasivejet systems currently producing useful byproducts simultaneously with the initial purpose of material removal. This is primarily due to the widespread acceptance of garnet as the preferred abrasive for almost all conventional applications.
A high-pressure pump is utilized to generate fluid pressure, usually above 30,000 psi, and preferably with water or water with additives as the liquid medium. The pressurized liquid is then transported at high velocities through tubing to a cutting head that mainly consists of an orifice to deliver the liquid, an abrasive feed tube, a mixing chamber where the liquid and abrasive are mixed, and a nozzle (sometimes called a focusing tube or a mixing tube) that finally directs the abrasivejet stream onto the subject material that is to be removed.
Currently, there are not any significant differences between any cutting heads or techniques of conventional abrasivejet equipment manufacturers, as generally all orifice, nozzle, and abrasive materials incorporated are the same for each manufacturer. Orifices are usually made from hard materials such as diamond or sapphire that generally produce a non-laminar jet. Nozzles are mostly made from a very hard tungsten carbide. Conventional abrasivejet equipment manufacturers also have similar cutting head designs with non-significant variations between each design. These cutting head designs have been widely demonstrated to cut at speeds within 30% of each other with similar surface finishes in comparative testing when equal parameters were used.
A more important similarity, as well as deficiency, of conventional abrasivejet technology is the widespread use of garnet abrasives over all other abrasives. Garnet is widely used because of its initial low cost and ability to cut a wide range of subject materials, however, it is widely used mainly because of its lower overall costs when compared to other conventional abrasives.
Conventional abrasivejet technology does not effectively use abrasives other than garnet due to numerous factors such as higher initial costs of most other hard abrasives compared to garnet and the inability of other hard abrasives to cut significantly faster than garnet. These factors generally result in higher overall costs of abrasive consumption after considering the final amount of material cut. There is also the limitation of conventional abrasivejet cutting head technology preventing use of harder abrasives than garnet because of the increased costs of accelerated nozzle wear created by these harder abrasives.
The similarities of conventional cutting head designs' primary use of only one type of nozzle material, use of only one abrasive medium, and use of only two types of orifice materials, mainly produce a common limitation of an approximate 3:1 nozzle to orifice ratio. This means the bore of the nozzle is generally three times larger than the diameter of the orifice. The volume of the abrasivejet stream inside the bore of the nozzle consists of an air, high-pressure liquid and abrasive mixture, with a relatively low amount of high-pressure liquid. The liquid is where the process energy originates in the cutting head. Therefore, a relatively larger volume of area of area in the nozzle bore compared to the smaller area of volume of the liquid energy creates inefficiencies.
A solution to create a more efficient use of energy would incorporate a smaller nozzle to orifice ratio such as 2:1 but this solution is not currently viable with use of conventional cutting heads and garnet abrasives. The best solution for conventional technology has been use of relatively small volumes of high-pressure liquid in the abrasivejet mixture allowing for variable cutting, but this also reduces the effective cutting energy by being dispersed over a greater area, hence, the effective energy is not optimally focused.
U.S. Pat. Nos. 3,424,386, 3,972,150, 4,080,762 and 4,125,969 all teach the abrasive (sand) stream to be in the central portion of the nozzle while the pressurized fluid is introduced into the peripheral area surrounding the central sand stream. A ring orifice plate or disk such as employed in the U.S. Pat. Nos. 3,424,386, 4,080,762 and 4,125,969 to provide the fluid jets around the sand stream has many disadvantages including: the introduction of pressurized fluid tangentially into a nozzle a short distance above the orifice disk is not conducive to the generator of a coherent fluid jet due to flow disturbances upstream of the orifices; sand in the central portion of a nozzle creates an abrasive environment that can weaken the interior wall of the annular fluid chamber without being detected; pressurized fluid in the outer annular space results in a nozzle that is very large in dimensions as both interior and exterior walls must be sized to accommodate the fluid pressure; and sealing the annular orifice disk can be very troublesome. The U.S. Pat. No. 3,994,097 teaches a central located water jet while sand is fed into a nozzle chamber through a single sand passageway. The sand is forced into the water jet by passage through a conical nozzle. This patent recognizes abrasion problems within the nozzle and the necessity of exact alignment. These problems would be intensified at higher pressures. All of these patients teach mixing abrasive into water by (1) intercepting an abrasive stream with water jets, and (2) forcing abrasives, water and air through a conical nozzle, without concern of fluid actions.
FIG. 1 of U.S. Pat. No. 5,184,434 depicts how the majority of abrasivejet cutting heads are currently designed. The problem areas with the prior art cutting head shown in this patent are the orifice, the mixing chamber and the liquid jet. The orifice is the device where the liquid jet passes through, building up to very high velocities. The mixing chamber is the area where abrasive joins with the liquid jet. A problem with this design is the separation effect of the jet as it starts to break up. The nozzle inlet then receives the stream at various angles and straightens it out while realizing considerable wear on its bore. FIG. 2 of U.S. Pat. No. 5,184,434 depicts the art of Abrasive Suspension Jet (sometimes called “Slurry Jet”) cutting. This methods adds abrasive to the stream before entering the orifice. The advantage of this method is that it produces a coherent jet, but the disadvantage is that components such as tubing, valves and orifices wear out quickly due to the abrasive suspension inside the system severely eroding everything it contacts.
Another disadvantage of the orifice designs in conventional abrasivejet is the sharp transition from the pump tubing to the relatively small orifice. This sharp transition creates a high resistance of the pressure flow and does not allow for property formed liquid optimization, resulting with jet distortion, and decrease in overall energy efficiency of the system.
Garnet is conventionally used because it does not wear the nozzles out significantly even with the non-laminar jet produced a conventional orifice as shown in FIG. 1 of U.S. Pat. No. 5,184,434, Garnet also has a low initial cost and it is effective in cutting a wide range of materials without significantly wearing the nozzles while using the standard 3:1 nozzle to orifice size ratio. These factors allow for a lower overall cost compared to other abrasives and have allowed garnet to be the primary abrasive medium used for almost all abrasivejet applications. However, there are many reasons why garnet is not the optimum abrasive available when considering the complete abrasivejet system, recycling and the ability to perform two or more processes in one operation.
One reason is that garnet is not the optimum abrasive is because it is not recyclable effectively. It is widely accepted that only 30% to 50% of larger garnet particles can be reclaimed for reuse after single cutting operation as most of the garnet particles are reduced in size from fracturing upon impact and made less effective for further cutting of subject materials. Current recycling processes of garnet generally add unused larger particles to the reclaimed particles in order to keep cutting speeds at an acceptable level.
Another disadvantage is that very hard subject materials such as carbides and hard ceramics are generally not cut with abrasivejet technology because of the very low cutting speed ability of garnet to cut these materials.
Thus it is readily apparent that there is a longfelt need for a multistage water jet cutting head that can cut subject materials more effectively by a high-pressure water jet mixed with abrasive particles in a multi-stage approach.